diff --git a/src/completion.cpp b/src/completion.cpp
new file mode 100644
index 0000000..44286e9
--- /dev/null
+++ b/src/completion.cpp
@@ -0,0 +1,26 @@
+/*
+ * Copyright (C) 2020 CESNET, https://photonics.cesnet.cz/
+ *
+ * Written by Václav Kubernát <kubernat@cesnet.cz>
+ *
+*/
+#include <boost/algorithm/string/predicate.hpp>
+#include <tuple>
+#include "completion.hpp"
+
+bool Completion::operator<(const Completion& b) const
+{
+    return std::tie(this->m_value, this->m_suffix, this->m_whenToAdd) < std::tie(b.m_value, b.m_suffix, b.m_whenToAdd);
+}
+
+bool Completion::operator==(const Completion& b) const
+{
+    return std::tie(this->m_value, this->m_suffix, this->m_whenToAdd) == std::tie(b.m_value, b.m_suffix, b.m_whenToAdd);
+}
+
+std::set<Completion> filterByPrefix(const std::set<Completion>& set, const std::string_view prefix)
+{
+    std::set<Completion> filtered;
+    std::copy_if(set.begin(), set.end(), std::inserter(filtered, filtered.end()), [prefix](Completion it) { return boost::starts_with(it.m_value, prefix); });
+    return filtered;
+}